Gasification of solid carbonaceous fuel



Jan. 8, 1957 w. GUMZ 2,776,875

GASIFICATION OF SOLID CARBONACEOUS FUEL Filed Jan. 2, 1952 v IN V EN TOR.

W/L EL M l/MZ BY filmy? Y5 United States Patent 2,776,879 GASIFICATION F SULID CARBGNACEOUS FUEL Wilhelm Gumz, Columbus, Ohio, assignor to Hydrocarbon Research, Inc, New York, N. Y.

Application January 2, 1952, Serial N 0. 264,451

2 Claims. (Cl. 48-202) This invention relates to a process for the gasification of a solid carbonaceous fuel. The process of'the invention is applicable to the gasification of coal, lignite, oil shale, and the like. It is particularly useful for the production of fuel gas from those carbonaceous materials which tend to agglomerate on heating.

The fluidized solids technique has been applied to processes for the gasification of carbonaceous materials. In such processes, small particles of the solid fuel are reacted with a gaseous reactant while the solid particles are maintained in a dense phase fluidized bed. Fluidization is effected by passing the reactant gases upwardly through a bed of the solid particles at a rate suflicient to agitate the particles but insuflicient for entrainment of the average size particles from the bed. The resulting bed of solid particles presents the appearance of a boiling liquid. Dense phase fluidization is now fairly well known in the art.

Coal, for example, in particle form, may be subjected to gasification in a fluidized bed by reaction with an oxidizing gas. Some difliculty has been experienced in the gasification of coal dueto the tendency of many grades of coal to form clinkers or agglomerate on heating. Some coals in particular, known as caking coals, have a tendency to become plastic or tacky on heating thereby causing agglomeration of the particles. These coals may be treated prior to gasification to prevent agglomeration. Such pretreatment may consist of heating the coal to drive off at least a portion of the volatilizable constituents therefrom, or partial preoxidation of. the coal, usually with an oxygen-containing gas or nitric acid. An expedient which is used to some extent involves mixing fresh coal with coke, ash, or an inert material, such as sand, to prevent agglomeration of the raw coal particles.

The process of the present invention is particularly adaptable to the handling of caking coals and similar solid fuels without difficulty due to the agglomerating tendency of the material and generally without the necessity for preliminary treating.

In accordance with this invention, the solid carbonaceous fuel is comminuted to a particle size suitable for fluidization, suitably less than 4 inch in diameter, and preferably less than about 0.2 inch in diameter, and charged to a gasification zone into an agitated mass of particles of hot char, or residue, resulting from previous partial gasification of coal. The bed of solids in the gasification zone is fluidized by a stream of flue gas so that carbonization of the feed material in the .resulting mixture takes place in a dense phase fluidized bed. Following charging of fresh coal and carbonization in a fluidized bed, fluidization of the bed of solids in the gasification reactor is discontinued and the bed permitted to settle. The'settled bed generally occupies a volume approximately /3 the volume of the fluidized bed. Fuel gas is generated by the gasification of the particles in the settled bed by reaction with a stream of steam passed downwardly through the settled bed of heated particles. Oxygen-containing gas may optionally be suppliedtothe 2,775,379 Patented Jan. 8, i957 through the bed of particles at a velocity suihcient to cause fluidization of the bed. These hot gases also supply heat to the bed to make up for heat lost therefrom by the endothermic reaction between carbon and steam during gasification. As the bed is fluidized, any agglomerate particles or clinkers settle to the bottom of the bed and are withdrawn therefrom. At the same time, an additional quantity of fresh coal is fed into the fluidized bed, thus completing the gasification cycle. I

The agglomerate particles removed from the gasification reactor are reacted with an oxygen-containing gas, suitably air, to supply heat in the process. During the fluidization, the stream of hot flue gases used for fluidization and for heating of the bed of solid particles in the gasifier is derived from the combustion of the agglomerate particles in a separate zone. When the particles in the gasification reactor are subjected to reaction with steam, the hot gases may be used to supply heat for the generation of steam or for other purposes.

An object of this invention is to provide an improved process for the gasification of a solid carbonaceous material. A further object is to provide such a process which is particularly applicable to the gasification of caking coal. Another object is to provide a process for the gasification of solid carbonaceous materials which tend to small particle size is fed from a storage hopper 6 by a v of the present invention.

screw conveyor 7 into a gasification vessel 8. The gasification vessel 8 is provided with a grate 9 that permits withdrawal of fairly large clinker particles to the space below the grate. It also permits gases to pas through but retains substantially all of the solid particles making up the charge in the gasification reactor. Grates of this type are known in the art and do not, per se, form a part Below grate 9, an outlet conduit 11 is provided for discharging gas from the gasification zone. A valve 12 closes the lower end of the gasification reaction vessel. When this valve is open it permits gases to enter the gasification reactor and also permits discharging solid particles from the gasification reactor, as will be described hereinafter. An inlet conduit 13 is provided at the upper end of vessel 8 for the introduction of a gasification reactant. Gases may also be discharged from the upper part of the vessel 8 through line 14. These gases may be cooled by a cooler 15 and may be treated in a separator is, suitably of the cyclone type, for the removal of powdered solids entrained in the gases. The resulting gases are discharged through line 17.

Disposed below vessel 8 is a separate reaction zone 20. Communication may be established between the flue gas generation zone 20 and the vessel 8 by opening valve 12. This permits flue gases from the combustion of residue in zone 2t) to pass into the gasification vessel 8. Alternatively, the gasesfrom zone 20 may be passed to a furnace 21 by operation of valve 22.

The furnace 21 may contain a more or less conventional boiler comprising steam generation tubes 23, steam drum 24, and steam preheating coils 25. Steam may from the gases.

be withdrawn from or supplied to the system through line 26. A part or all of the steam introduced into vessel 8 through line 13 may be supplied from the steam boiler through line 27;

Air is supplied to the lower portion of zone from a blower 31 through tuyeres 32 for consumption of fuel therein. Ash is discharged from zone 20 through an outlet 33. Air from blower 31 may also be introduced through tuyeres 3d into zone 20 above the level of the fuel therein, as illustrated in the drawings and, if desired, to an outlet 36 in the furnace 21.

Fines separated from the gas stream in separator 16 i may be introduced through line 37 into Zone, 20. -Additional fuel may be discharged, if necessary, from a storage bin 38 into zone 29 through line 39.

' In operation, air is blown through tuyeres 32 into the flue gas generation zone 20 consuming carbon from the fuel and producing hot producer gas. Additional air is introduced through tuyeres 34 to burn the producergas with a substantial excess of secondary air.l The hot gases from zone 20 are introduced into vessel 8,-belowgrate 9 by opening valve 12. Valve 22 is in closed position. Grate 9 allows free entrance of the hot gases from zone 24), which fluidizes the fuel bed A1, increasing itsvolume to about /3 the volume of vessel 3, as indicated by A2.

During this period, fresh coal is introduced to vessel 8 from hopper 6 by means of feeder 7. Gases discharged from vessel 3 through duct 14 are cooled by acooler 15, suitably in the form of a waste boiler, and passed to cyclone separator 16 where fine particles are separated The gases are discharged from the system through line 17. Fine particles separated from the gases are passed through line 37 to zone 20.

During the period in which gases are passed from zone 20 through the bed of fuel in vessel 8, agglomerate particles settle to the bottom of the fuel bed and escape from the bed through grate 9. These particles drop into zone 20 and provide a source of fuel for this portion of the process.

When the temperature of the fuel bed in vessel 8 is raised to the desired temperature, for example, 1,600 F. to 2,000 E, valve 12 is closed and valve 22 opened to permit the gases from zone 20 to pass into furnace- 21. Air is continuously introduced into zone 20 to produce heat. This heat is now utilized in furnace 21 for the production of steam, as explained in more detail hereinafter.

Instead of superheater tubes 25, a regeneration chamber with checker brickwork, not illustrated in the drawings, may be used for preheating steam, as is well known in the art. An alternative, though less desirable, procedure is the operation of the gas generation in vessel 8 as a fluidizing system. The downdraft-fixed bed operation and the fluidized bed operation may be used consecutively in the gas producing cycle.

Some of the advantages of theprocess of-my-invention as compared. with usual water gas producersare: higher average bed temperatures, hence higher gas yields; less carbon dioxide; longer gasification periods; and less danger of-damaging the grates. Unclassified, lower grade fuels may be used, which results in lower fuel cost and, consequently, lower gas cost. Furthermore, the system may be operated under high pressure.

Apparatus for operation under pressure is illustrated diagrammatically in Figure 2. In this case, theqwater gas generator 8 is designed for operation underpressure, for example, from 300 to 750 pounds per square inch gauge. The flue gas generation zone 29 may be designed for operation at the samepressure or a lower pressure, e. g., atmospheric pressure. The two zones are connected by a pressure lock 40 provided with a valve 41 communicating with the lower part of vessel 8 and valve 42 communicating with'the upper part of vessel 20.

Alternatively, the pressure lock 40 may be omitted and the pressure in vessel 20 increased to, that in vessel 8 during the heating period and subsequently decreased v for discharging the ash or slag from the vessel.

t able to operate gasification zone 20 at a temperature Upon discontinuing the introduction of gas through valve 12, the fuel bed in vessel 8 settles above grate 9 ,.such that the ash is removed as afluid slag.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and,

therefore, only such limitations should be imposed as are indicated in the appended claims.

Iclaim:

.1. In a cyclic process for the production of fuel gas from a solid carbonaceous fuel wherein a gaseous reactant comprising steam is reacted with said fuel at a gasification reaction temperature within the range of from about 1500 F. to about 2000 F. to produce a fuel gas comprising carbon monoxide and hydrogen as principal constituents, the flow of reactant gas is periodically inter- .rupted and heat supplied tosaid bed, the improvement which comprises passing said gaseous reactant downwardly so that the steam passes down through the hot fuelbed generating fuel gas. The fuel gas leaves through grate 9, and is discharged from the vessel through line 11, which is now open.

" When the fuel'bcd temperature drops to a temperathr'ough a bed of said solid fuel in a gas generation zone during the period of gas generation, thereafter disconture such that the rate of gas production falls off, for

example, 1,500 E, the flow of steam through line. 13 is discontinued, line 11 is closed, line 14 and valve 12 opened, valve 22 closed; and the cycle repeated.

While gas is being made in vessel 8 by reacting the fuel bed with steam, the hot gases produced in the gas production zone 20 arepassed through valve 22 into furnace 21 to produce steam for the process." Steam may be generated in the boiler tubes 23 and this steam tinuing ,the flow ofsaid reactant gas through said had, supplying heat to said bed by introducing a stream of hot flue gas at a temperature above said reaction temperature into the lower portion of said bedand passing the flue gas upwardly therethrough at a rate sufi'icient to maintain the solid particles in said bed in a state of dense phase fluidization whereby fine particles are entrained insaid gas stream and the largest size particles in 'said had gravitate to the lower portion of said bed, removing said largest sizenparticles from the lower portion of said bed, introducing fresh fuel into said bed only during fiuidization thereof, separating said fine particles from said gas stream, burning said largest size particles and said fine particles with air in a separate zone to supply said stream of hot fluev gas, and thereafter discontinuing the flow of hot .fiue, gas through said bed and again passing said gaseous Q reactant downwardly therethrough for the generation of fuel gas.

2. Ina cyclic process for the production of fuel gas from a solid carbonaceous fuel wherein agaseous reactant t comprising steam is reacted with said fuelat; a gasification reaction temperature within the range of from about 1500 F. to about 2000 F. to produce a fuel gas comprising carbon monoxide and hydrogen as principal constituents, the flow of reactant gas is periodically interrupted and heat supplied to said bed, the improvement which comprises passing said gaseous reactant downwardly through a bed of said solid fuel in a gas generation zone during the period of gas generation, thereafter discontinuing the flow of said reactant gas through said bed, supplying heat to said bed by introducing a stream of hot flue gas at a tem- 1 perature above said reaction temperature into the lower portion of said bed and passing the flue gas upwardly therethrough at a rate sufficient to maintain the solid particles in said bed in a state of dense phase fluidization whereby the larger particles in said bed gravitate to the lower portion of said bed, removing the larger particles from the lower portion of said bed, introducing fresh fuel into said bed, burning said particles removed from the lower portion of said bed with air to supply said stream of hot flue gas, and thereafter discontinuing the flow of hot flue gas through said bed when said bed is at a temperature in the range aforesaid and again passing said reactant gas downwardly therethrough for the generation of fuel gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,808,672 Lynn June 2, 1931 1,913,968 Winkler June 13, 1933 2,099,968 Szikla Nov. 23, 1937 2,126,150 Stryker Aug. 9, 1938 2,361,292 Hunter et a1 Oct. 24, 1944 FOREIGN PATENTS 9,327 Great Britain June 5, 1889 285,004 Great Britain Mar. 31, 1928 306,614 Great Britain Feb. 28, 1929 318,016 Great Britain Aug. 29, 1929 

2. IN A CYCLIC PROCESS FOR THE PRODUCTION OF FUEL GAS FROM A SOLID CARBONACEOUS FUEL WHEREIN A GASEOUS REACTANT COMPRISING STEAM IS REACTED WITH SAID FUEL AT A GASIFICATION REACTION TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 1500* F. TO ABOUT 2000* F. TO PRODUCE A FUEL GAS COMPRISING CARBON MONOXIDE AND HYDROGEN AS PRINCIPAL CONSTITUENTS, THE FLOW OF REACTANT GAS IS PERIODICALLY INTERRUPTED AND HEAT SUPPLIED TO SAID BED, THE IMPROVEMENT WHICH COMPRISES PASSING SAID GASEOUS REACTANT DOWNWARDLY THROUGH A BED OF SAID SOLID FUEL IN A GAS GENERATION ZONE DURING THE PERIOD OF GAS GENERATION, THEREAFTER DISCONTINUING THE FLOW OF SAID REACTANT GAS THROUGH SAID BED, SUPPLYING HEAT TO SAID BED BY INTRODUCING A STREAM OF HOT FLUE GAS AT A TEMPERATURE ABOVE SAID REACTION TEMPERATURE INTO THE LOWER PROTION OF SAID BED AND PASSING THE FLUE GAS UPWARDLY THERETHROUGH AT A RATE SUFFICIENT TO MAINTAIN THE SOLID PARTICLES IN SAID BED IN A STATE OF DENSE PHASE FLUIDIZTION WHEREBY THE LARGER PARTICLES IN SAID BED GRAVITATE TO THE LOWER PORTION OF SAID BED, REMOVING THE LARGER PARTICLES FROM THE LOWER PORTION OF SAID BED, INTRODUCING FRESH FUEL INTO SAID BED, BURNING SAID PARTICLES REMOVED FROM THE LOWER PORTION OF SAID BED WITH AIR TO SUPPLY SAID STREAM OF HOT FUEL GAS, AND THEREAFTER DISCONTINUING THE FLOW OF HOT FLUE GAS THROUGH SAID BED WHEN SAID BED IS AT A TEMPERATURE IN THE RANGE AFORESAID AND AGAIN PASSING SAID REACTANT GAS DOWNWARDLY THERETHROUGH FOR THE GENERATION OF FUEL GAS. 